Electrical humidity-sensing unit



United States Patent ELECTRICAL HUMIDITY-SENSING UNIT Carlton E.Ohiheiser, Silver Spring, Md., assignor to American Instrument Company,Inc., Silver Spring,

Application February 20, 1956, Serial No. 566,453

9 Claims. (Cl. 20163) This invention relates to electrical humiditysensing units, and more particularly to a humidity sensing unitemploying a humidity-responsive resistance element of the typecomprising a body of porous ceramic material.

A main object of the invention is to provide a novel and improvedelectrical humidity sensing unit which is simple in construction, whichis compact in size, and which is arranged so that the resistance elementthereof may be readily inserted or removed whenever required.

A further object of the invention is to provide an improved electricalhumidity sensing unit of the resistance type which is relativelyinexpensive to manufacture, which is highly resistant to mechanicalshock and vibration, and which is stable in performance.

A still further object of the invention is to provide an improvedelectrical humidity sensing unit which may be made in a very small sizeso that it can be employed in locations where space is limited, which isrugged in construction, and which possesses substantially the sameaccuracy, as units of much larger size.

Further objects and advantages of the invention Will become apparentfrom the following description and claims, and from the accompanyingdrawings, wherein:

Figure 1 is a greatly enlarged front elevational view, partly incross-section, of an improved electrical humidity sensing unitconstructed in accordance with the present invention.

' Figure 2 is a bottom view of the humidity sensing unit of Figure 1.

Figure 3 is a cross-sectional view taken on the line 3+3 of Figure 2.

Figure 4 is a cross-sectional view taken on the line 4-4 of Figure 3.

Figure 5 is a front elevational view of the humidityresponsiveresistance element employed in the unit of Figures 1 to 4, drawnsubstantially to the same scale as said figures.

Figure 6 is a side elevational view of one of the leaf spring contactmembers employed in the unit of Figures 1 to 4, drawn substantially tothe same scale as said figures.

Referring to the drawings, wherein a typical humidity sensing unitaccording to this invention is illustrated to a greatly enlarged scale,the unit is designated generally at 11. Said unit comprises a relativelyfiat, sleeve-like housing 12 of insulating material, such as a suitableplastic material, which may be, for example, generally rectangular inshape, but which obviously may have any other desired shape.

In the typical embodiment illustrated in the drawings, the housing 12comprises a pair of substantially right angled molded plastic bodies 17and 18 having the major flanges 13, 13' and the relatively short minorflanges 14, 14 extending at right angles to said major flanges. Theright angled bodies are secured together, as by suitable cement, withthe edges of the minor flanges abutting the Lit 2,859,318 Patented Nov.4, 1958 inside margins of the major flanges, to define the aforesaidsleeve-like housing.

The inside portions of the major flanges 13, 13' are formed withintermediate longitudinal grooves or channels 15, whereby opposing sidegrooves 16, 16 are defined inside the housing cavity on opposite sidesof the channels 15, as shown in Figure 4.

Each body 17 and 18 is formed on the inner surface of its major flangewith respective integral stop lugs 19, 19 located at one end of thehousing 12 at opposite sides of the channels 15, whereby a pair of stoplugs 19, 19 serves as a positioning means for the humidity-responsiveresistance element 20 contained in the housing, as will be presentlydescribed.

Disposed longitudinally in the respective side grooves 16, 16 andbearing on the inside surface of the flange 13' on opposite sides of itschannel 15 are respective conductive leaf springs 21, 21, each springcomprising a flat intermediate portion and respective arcuately curvedresilient leaf portions 22, 22 integrally connected to the ends of theflat intermediate portion. The flat intermediate portions of the leafsprings are laterally extended with respect to the leaf portions 22, 22,as shown at 23, and are received in respective rectangular recesses 24,24, formed in the intermediate portions of the grooves 16, 16. Thelaterally extended portions 23 are formed with respective right-angledlugs 25 which engage the inside surfaces of the associated recesses 24,as shown in Figure 4. Respective insulated conductors 26, 26 extendaround the upper side portions of the housing 12 and enter the flanges14 and 14' through apertures 27 provided sub stantially centrally insaid flanges. The terminals of the conductors 26, 26 are electricallyconnected, as by soldering, as by soldering, to the respective lugs 25,25.

The humidity-responsive resistance element 20 comprises a relativelyflat rectangular body 28 of humiditysensitive resistance material, forexample, porous unglazed red pottery clay, such as described in U. S.Patent No. 2,358,406 to Fred Lichtgarn, or any of the other porousceramic materials described in said patent, for example, a mixture whichincludes finely divided material of relatively high conductivity. Thismixture is capable of adsorbing water vapor from the atmosphere indirect relation to the relative humidity, producing a change inelectrical conductivity of the material.

The side marginal portions of the body 28 are each suitably coated witha' layer 29 of conductive material, as shown in Figure 5, said layers 29preferably extending around the longitudinal edges of body 28 anddefining electrodes at said longitudinal edges.

As shown, the element 20 is of suflicient width and thickness so that itis receivable in the sleeve-like housing 12 with the electrode portions29 thereof disposed in the respective side grooves 16, 16 and thesurfaces of said electrode portions clampingly and conductively engagedby the resilient portions 22, 22 of the respective leaf springs 21, asshown in Figures 2, 3 and 4. Thus, each leaf spring 21 clampingly andconductively engages a respective electrode 29 and is thus electricallyconnected to one side margin of element 20 while frictionally securingthe element in the sleeve-like housing 12 with the end of the element inabutment with a pair of stop lugs 19, 19.

The channels 15, 15 allow the atmosphere to circulate longitudinallythrough the unit around the humiditysensitive resistance element 20. Theouter walls of said channels are further formed with a plurality oflongitudinally spaced circular apertures 30 which directly expose themajor surfaces of the element 20 to .the atmosphere.

The leaf springs 21, 21 are permanently secured in the side grooves 19,19 by the soldered connections, shown at 31, 31 of the terminals ofconductors 26, 26 to the lugs 25, 25. However, the humidity-responsiveresistance element 20 may be removed and replaced, as required, throughthe open end of the sleeve-like housing 12 opposite the positioning lugs19. This allows the housing or holder 12 to be employed withhumidityresponsivee resistance elements 20 having different operatingranges, and also allows an element to be readily replaced whenever ithas become damaged or is otherwise unsuitable for further use.

While a specific embodiment of an improved humidity sensing unit hasbeen disclosed in the foregoing description it will be understood thatvarious modifications within the spirit of the invention may occur tothose skilled in the art. Therefore it is intended that no limitationsbe placed on the invention except as defined by the scope of theappended claims.

What is claimed is:

1. An electrical humidity sensing unit of the resistance type comprisinga housing of insulating material formed with opposing parallel internalgrooves and being apertured between said grooves, respective conductivespring members disposed in said grooves, respective terminal conductorsconnected to said spring members and extending outside the housing, anda body of humidity-sensitive resistance material slidably disposed insaid housing and being clampingly and conductively engaged at itsopposite margins by said spring members.

2. An electrical humidity sensing unit of the resistance type comprisinga housing of insulating material formed with opposing parallel internalgrooves and being apertured between said grooves, respective conductiveleaf springs disposed in said grooves, respective terminal conductorsconnected to said leaf springs and extending outside the housing, and abody of humidity-sensitive resistance material slidably disposed in saidhousing and being clampingly and conductively engaged at its oppositemargins by said leaf springs.

3. An electrical humidity sensing unit of the resistance type comprisinga housing of insulating material formed with opposing parallel internalgrooves and being apertured between said grooves, respective conductivespring members disposed in said grooves, respective terminal conductorsconnected to said spring members and extending outside the housing, anda body of porous ceramic material whose electrical resistance varieswith humidity slidably disposed in said housing, said body havingsubstantially parallel opposite side margins and being clampingly andconductively engaged at said opposite side margins by said springmembers.

4. An electrical humidity sensing unit of the resistance type comprisinga relatively flat housing of insulating material open at least at oneend and formed with opposing parallel internal grooves at its oppositeside portions and being apertured between said grooves, respectiveconductive leaf springs disposed longitudinally in said grooves,respective terminal conductors connected to said leaf springs andextending outside the housing, and a relatively flat rigid body ofhumidity-sensitive resistance material slidably disposed in saidhousing, said body having substantially parallel opposite side marginsand being clampingly and conductively engaged at said opposite sidemargins by said leaf springs.

5. An electrical humudity-sensing unit of the resistance type comprisinga relatively flat, sleeve-like housing of insulating material formedwith opposing internal grooves at its opposite side portions, respectiveconductive leaf springs disposed longitudinally in said groovessubstantially parallel to the major walls of the housing, at least oneof said major walls being formed between said grooves with an internalchannel to allow air to move longitudinally through the housing,respective terminal elements electrically connected to the leaf springsand extending outside the housing, and a relatively flat rigid body ofhumidity-sensitive resistance material disposed in said housing, saidlast-named body having substantially parallel opposite side edges andbeing of suflicient Width so that its side edges are slidably receivedin said grooves and being of suflicient thickness so that its sidemarginal portions are clampingly and conductively engaged by said leafsprings.

6. The structure of claim 5, and wherein said one major wall isapertured at said channel to directly expose a face of said body to theatmosphere at said one major Wall.

7. An electrical humidity-sensing unit of the resistance type comprisinga relatively flat, sleeve-like housing of insulating material formedwith opposing internal grooves at its opposite side portions, respectiveconductive leaf springs disposed longitudinally in said groovessubstantially parallel to the major walls of the housing, at least oneof said major walls being formed between said grooves with an internallongitudinal channel to allow air to move longitudinally through thehousing, said grooves being respectively formed at their intermediateportions with recesses, respective retaining lugs formed on said leafsprings and lockingly engaging in said recesses, respective terminalconductors electrically connected to said lugs and extending outside thehousing, and a relatively flat body of humidity-sensitive resistancematerial disposed in said housing, said last-named body being ofsufiicient width so that its side edges are received in said grooves andbeing of suificient thickness so that its sidemarginal portions areclampingly and conductively engaged by said leaf springs.

8. The structure of claim 7, and wherein said one major wall isapertured at said channel to directly expose a face of said body to theatmosphere at said one major wall.

9. The structure of'claim 8, and abutment means in one end portion ofthe housing engageable with an end of said body to limit movement of thebody toward said one end portion of the housing.

References Cited in the file of this patent UNITED STATES PATENTS678,990 Swoboda July 23, 1901 2,047,638 Kott July 14, 1936 2,297,323Reeo Sept. 29, 1942 2,731,586 Born Jan. 17, 1956 FOREIGN PATENTS 505,721Canada Sept. 14, 1954

